The quality of phosphate coatings before cataphoretic dip lacquering (CDL) depends upon a number of parameters, including physical parameters, such as the shape and size of the crystals, their mechanical stability and, in particular, the free metal surface after phosphating, the so-called pore area. Among the chemical parameters, alkali stability during cataphoretic coating, the binding strength of the water of crystallization of the zinc phosphate crystals during stoving of the lacquers and the rehydration capacity are of particular interest.
The weight of the coating can be controlled and, in particular, reduced by using activating agents before phosphating. Active centers from which crystal growth advances are formed on the metal surface by the polymeric titanium phosphates present in the activating agents. On the one hand, this results in smaller and mechanically more stable crystals, on the other hand the pore area is reduced in size which makes it more difficult for corrosive media to attack the lacquer coating in the event of damage.